1. Field of the Invention
The present invention relates to a process for selectively preparing severely sterically hindered secondary aminoether alcohols by reacting a primary amino compound with a polyalkenyl ether glycol in the presence of a hydrogenation catalyst at elevated temperatures and pressures. The severely sterically hindered secondary aminoether alcohols are useful in acid gas scrubbing processes, particularly in the selective removal of H.sub.2 S from gaseous streams containing CO.sub.2 and H.sub.2 S.
2. Description of Related Patents and Publications
Recently, it was shown that severely sterically hindered secondary aminoether alcohols are superior to methyldiethanolamine (MDEA) in scrubbing H.sub.2 S from gaseous streams containing the same, especially in selectively removing H.sub.2 S from normally gaseous mixture containing CO.sub.2 and H.sub.2 S. Such processes are disclosed and claimed in U.S. Ser. No. 339,891, filed Jan. 18, 1982, now U.S. Pat. No. 4,405,585, the disclosure of which is incorporated herein by reference. These compounds may be produced by processes such as reacting a primary amine having a bulky carbon atom grouping with a haloalkyoxyalkanol. This process is more fully disclosed in allowed U.S. Ser. No. 339,892, filed Jan. 18, 1982, and allowed U.S. Ser. No. 453,452 filed Dec. 27, 1982, the disclosures of which are incorporated herein by reference. One disadvantage inherent in the use of haloalkoxy-alkanols is the need to employ corrosion-resistant equipment due to formation of halide by-products and the necessity to remove these halide by-products. Also, such processes require numerous purification steps including the use of caustic for the conversion of by-product amine hydrochloride salts into inorganic chloride and a subsequent filtration. Such purification procedures contribute to increasing the costs in producing the desired amine product. In addition, disposal of large quantities of inorganic chlorides produced in this process may present environmental problems.
The amination of alcohols with ammonia, primary and secondary amines by hydrogenation-dehydrogenation catalysis is well known as evidenced by ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Vol. 2, 3rd Edition, p.276. However, very bulky amines appear ineffective in this process.
U.S. Pat. No. 3,223,734 states that amines with branching at the carbon adjacent (alpha) to the amino moiety are much less preferred for the amine/alcohol amination process due to the inferior results with such reactants. U.S. Pat. No. 3,366,687 describes the viability of the amination process using the alpha-branched isopropylamine. There is no disclosure of using the more bulky tertiary alkyl groups in the amination reaction.
Both U.S. Pat. Nos. 3,223,734 and 3,366,687 disclose that barium promoted copper chromite catalysts are capable of giving yields of greater than 60% from the amine/alcohol amination process. Baiker and Richarz, Tetrahedron Lett, 1937 (1977), reported that the dimethylamine/alcohol reaction operated in a continuous mode (fixed-bed reaction) to give over 96% conversion to tertiary amine when a copper-chromium oxide catalyst (BASF H3-107) was used. Murahask, Chem. Comm., 931 (1974), has described the use of palladium black to catalyze, in 98% yield, the amination of benzyl alcohol with C.sub.6 amines.
In contrast to these disclosures, applicants have found that barium promoted or unpromoted copper chromite and palladium black catalysts do not catalyze the reaction of bulky amines such as tertiary butylamine with diethylene glycol.
The present invention is based on the discovery that when a primary amino compound having steric hindrance is reacted with a polyalkenyl ether glycol or a primary amino compound is reacted with a polyalkenyl ether glycol having steric hindrance in the presence of a hydrogenation-dehydrogenation catalyst, a severely sterically hindered secondary aminoether alcohol is produced. Unexpectedly, the resulting severely sterically hindered secondary aminoether alcohol will not react further with additional glycol reactant to form a tertiary amine even when excess glycol reactant is used. This is in contrast with other processes involving the amination of polyalkenyl ether glycols with primary amino compounds, which typically provide tertiary amines.